1. Field of Invention
The present invention relates to a semiconductor device and a method of forming the same, and more generally to a semiconductor device having a micro-electromechanical system (MEMS) device and a method of forming the same.
2. Description of Related Art
A MEMS device is a device fabricated by using a micro-machining technique. Due to its advantages of light weight and small size, the MEMS device well satisfies the current requirements for light, thin, short, and small electronic products, and is studied in many fields. The existing MEMS devices include accelerometers, switches, capacitors, sensors, microphones, and other ultra small-sized electromechanical devices.
MEMS microphones fabricated by using the MEMS technique have advantages of light weight, small size, and desirable signal quality, and therefore become the mainstream of miniature microphones. In the process of forming a MEMS microphone, after a MOS device and a MEMS device are formed on a substrate, a portion of the substrate at the backside of the MEMS device is removed to form a cavity therein. However, silicon grass is often observed after the cavity forming step. Such silicon grass is undesirable and may deteriorate the MEMS performance.